What is it?
Psoriasis is a long term autoimmune disease that causes patches of abnormal skin. There are five types of psoriasis, but the one accounting for 90% of cases, psoriasis vulgaris, is characterized by red patches with white scales on top. The patches are often itchy, and they can be present in a small area or even cover the whole body.
Psoriasis affects around 2-4% of the population of the Western world, and typically makes it first appearance between ages 15-25.
What causes it?
While the cause of psoriasis is not fully understood, a number of persuasive theories exist. The truth presumably lies somewhere between genetics, the immune system, and environmental factors.
Research has found that the twin siblings of people with psoriasis are 70% likely to develop it themselves. This suggests a strong yet not deterministic genetic link. Chronic infections, stress, and changes in climate are some of the things associated with the worsening of the disease.
What happens during it?
The cells in our skin’s outer layer get renewed about once a month. In psoriasis this process speeds up with around five times. The body can’t keep up with this, and immature cells pile up on the skin surface causing the characteristic patches covered with dead cells.
Why the cell turnout rate is so high is closely tied to the immune system. The T cell is a type of white cells, and its main jobs include recognizing and helping to destroy cells that have been infected with things like viruses. If the T cells notice something that attempts to invade the body, they start producing cytokines: inflammation-causing molecules that make the blood vessels in the infected area dilate and in that way increase the amount of white cells transported there.
Psoriasis is called an autoimmune disease because it is caused by the body’s own immune cells attacking the body’s healthy cells by accident. It is believed that the activation of the T cells is a vital part of a series of reactions that eventually leads to the inflammation of a skin area. The produced cytokines provoke keratinocytes, the cells of the skin’s outer layer, to divide and thus renew themselves excessively often. A cycle begins, when the T cells cause keranocytes to die and as a response they start dividing more rapidly, which triggers the development of new T cells.
How can it be treated?
While there is no definite cure for psoriasis, the symptoms can be managed. There are three main kinds of treatment: topical creams and such applied on the skin, phototherapy where ultraviolet light is used to slow down the renewal of cells, and systemic treatment where oral or injected medications are used.
Sources: http://www.webmd.com/skin-problems-and-treatments/psoriasis/psoriasis-causes-triggers, https://www.psoriasis.org/research/science-of-psoriasis/immune-system, http://emedicine.medscape.com/article/1943419-overview, en.wikipedia.org/wiki/Psoriasis, http://www.nhs.uk/Conditions/Psoriasis/Pages/Introduction.aspx, https://www.psoriasis.org/research/science-of-psoriasis/immune-system, http://www.webmd.com/skin-problems-and-treatments/psoriasis/phototherapy-for-psoriasis